Crash Report: http://pastebin.com/XevxzGSv

I know Buildcraft is the problem because when I uninstall it everything works fine!

Thanks in advance ^^

Its not BC problem. One of your mods includes old BC API. It vanishes after you remove BC as nothing is then using it.

Oh I see. Does the report have any information on what mod that is or do I have to, sadly, go through the mods and see which one it is?

Unfortunately it doesn't. You might want to look into mods jars for folder buildcraft.
Just remove this folder from jar (leave it in buildcraft itself) and restart MC. If it won't crash you've found it.

Issue solved!
It was Universal Electricity. Thanks @Kubuxu :D